Circuit Diagrams

Circuit Symbols

Warning: This lesson might include some technical words without definition. These will be covered in subsequent lessons in this topic, though feel free to do a cheeky google yourself first!

Circuit diagrams use standard symbols to represent a circuit component, as shown below.

Circuit Diagrams, figure 1

It is vital that you are able to recall and draw each of the circuit symbols. These are easy marks to pick up in an exam.

Each component has a different function:

  1. Switch (Open or Closed): Switches are used as an easy way to make or break a circuit, turning it on or off.
  2. Cell: Cells give power to the circuit, they store chemical energy. In everyday life, lots of people incorrectly call these batteries.
  3. Battery: Batteries are two or more cells in a circuit together.
  4. Diode: A diode only allows the current to flow one way. There are different types of diode, one of which we will meet later on.
  5. Resistor: A resistor provides a constant resistance to the circuit. This is important if you want to have a specific current or potential difference running through other components in the circuit.
  6. Variable Resistor: A resistor where you can change its resistance. They often have a dial to allow the resistance to be changed.
  7. LED: This stands for a light emitting diode. Remember what a diode does? This is a special kind of diode which releases light. LEDs are often used in torches and lights in a home.
  8. Lamp: Also known as a bulb and releases light when energy passes through it.
  9. Fuse: A fuse is a safety component. If the current becomes to high, it melts and breaks the circuit preventing a fire or damage. This is discussed in more detail in a further lesson.
  10. Voltmeter: Used to measure potential difference, this is always placed in parallel
  11. Ammeter: Used to measure current, this is always placed in series.
  12. Thermistor: A resistor changes its resistance according to its temperature. This is discussed in more detail in a further lesson.
  13. LDR: Light dependent resistor: This resistor changes its resistance according to how much light is shone onto it. This is discussed in more detail in a further lesson.

Drawing Circuits

Drawing circuits is relatively simple so long as you follow the following general rules:

  1. Read the instructions carefully!!! I cannot tell you how many times students do not read the question properly and get it wrong.
  2. Reread rule 1!
  3. Use a ruler
  4. Always ensure that there is either a battery or a cell drawn correctly.
  5. If an ammeter is required, always draw it as part of the same loop as the battery/cell.
  6. If a voltmeter is required, draw it around the component that you need to measure e.g. bulb or resistor

Look at the circuit below. It has an ammeter in the same loop as the cell and the voltmeter is around or across the resistor.

Circuit Diagrams, figure 1

In any question where you need to interpret a circuit diagram, make sure that everything it connect correctly like the steps above.